Effect of electron donors on CO2 fixation from a model cement industry flue gas by non-photosynthetic microbial communities in batch and continuous reactors

Abstract

The aim of this work was to evaluate the effect of different inorganic compounds as electron donors for the capture of CO₂ from a model cement flue gas CO₂ /O₂ /N₂ (4.2:13.5:82.3% v/v) using a non-photosynthetic microbial community. The inoculum obtained from a H₂ -producing reactor was acclimated to CO₂ consumption achieving 100% of CO₂ removal after 45 days. Na₂ S, MnCl₂ , NaNO₂ , NH₄ Cl, Na₂ S₂ O₃ , and FeCl₂ were used as energy source for CO₂ fixation by the acclimated microbial community showing different efficiencies, being Na₂ S the best electron donor evaluated (100% of CO₂ consumption) and FeCl₂ the less effective (28% of CO₂ consumption). In all treatments, acetate and propionate were the main endpoint metabolites. Moreover, scaling the process to a continuous laboratory biotrickling filter using Na₂ S as energy source showed a CO₂ consumption of up to 77%. Analysis of the microbial community showed that Na₂ S and FeCl₂ exerted a strong selection on the microbial members in the community showing significant differences (PERMANOVA, p = 0.0001) compared to the control and the other treatments. Results suggest that the CO₂ fixing pathways used by the microbial community in all treatments were the 3-hydroxypropionate-4-hydroxybutyrate cycle and the Wood-Ljungdahl pathway.